Acrylonitrile-butadiene-styrene (ABS) type resins are generally used in electrical appliances, parts of vehicle or the like because of their good balance of properties of the components, e.g., processability of styrene, chemical resistance of acrylonitrile and impact strength of butadiene.
At present, there have been a lot of efforts to improve impact strength of the acrylonitrile-butadiene-styrene type resins. For example, one method for preparing the ABS resin is accomplished by the emulsion polymerization of rubber particles prepared by continuous polymerization as disclosed in U.S. Pat. Nos. 4,430,478; 5,605,963; 5,696,204; and so on.
However, the conventional high impact ABS resin has the weakness of deteriorated dimensional stability of the resin due to increasing linear thermal expansion coefficient. For example, if a product employing the resin is exposed to rapid changes of ambient temperatures, the product may crack due to repetitive stress caused by thermal expansion and contraction of the product. This mainly occurs in cases where the resin is applied in internal or external materials of vehicles.
In order to lower linear expansion coefficient and minimize dimensional changes caused by thermal changes, inorganic fillers are typically used. Especially, a lot of glass fiber is used to increase modulus and thermal resistance of the resin. Although this kind of conventional method can lower the linear expansion coefficient, the surface gloss of the ABS resin as a result of the inorganic filler is too poor to be used in external materials.
U.S. Pat. Nos. 4,816,510 and 5,965,655 disclose lowering linear expansion by applying mica or wollastonite to polyphenylene ether or polycarbonate resin. However, this results in lower impact strength of the resin.
Another conventional method minimizes the amount of rubber elastomer in the ABS resin and adds N-phenyl maleimide copolymer to the ABS resin in order to improve heat resistance and dimensional stability of the ABS resin. Although employing N-phenyl maleimide gives the resin improved heat resistance, this method cannot lower the linear thermal expansion coefficient of the resin.
In order to use the ABS resin in external materials of vehicles which may undergo rapid temperature changes, the ABS resin should have a low coefficient of linear thermal expansion, high impact strength and good surface gloss for post-processes such as coating and plating.